Remove unnecessary set_name! calls in resolutions and presentations (…

…#3815)

* Comment out some unreachable code

* Remove unnecessary `set_name!` calls in resolutions and presentations

* Add missing parentheses

experimental/DoubleAndHyperComplexes/src/Objects/Methods.jl

@@ -296,7 +296,7 @@ function _free_show(io::IO, C::AbsHyperComplex)
   R = Nemo.base_ring(C[first(rng)])
   R_name = AbstractAlgebra.get_name(R)
   if isnothing(R_name)
-    R_name = "$R"
+    R_name = "($R)"
   end
 
   for i=reverse(rng)

src/Modules/UngradedModules/FreeMod.jl

@@ -93,6 +93,9 @@ end
 # un-named free module over a named ring X will acquire the name 
 # X^r
 function AbstractAlgebra.extra_name(F::FreeMod)
+  if rank(F) == 0
+    return "0"
+  end
   s = AbstractAlgebra.get_name(base_ring(F))
   if s !== nothing
     return "$s^$(rank(F))"

src/Modules/UngradedModules/FreeResolutions.jl

@@ -13,7 +13,7 @@ function free_show(io::IO, C::ComplexOfMorphisms)
   R = Nemo.base_ring(C[first(rng)])
   R_name = AbstractAlgebra.get_name(R)
   if isnothing(R_name)
-    R_name = "$R"
+    R_name = "($R)"
   end
 
   for i=reverse(rng)
@@ -199,12 +199,6 @@ function _extend_free_resolution(cc::Hecke.ComplexOfMorphisms, idx::Int)
   #= adjust length for extension length in Oscar =#
   slen = slen > len ? len : slen
 
-  br_name = AbstractAlgebra.get_name(base_ring(kernel_entry))
-  if br_name === nothing
-    br_name = "R"
-  end
-
-
   while j <= slen
     rk = Singular.ngens(res[j])
     if is_graded(dom)
@@ -214,12 +208,10 @@ function _extend_free_resolution(cc::Hecke.ComplexOfMorphisms, idx::Int)
       #map = graded_map(codom, SM.matrix) # going via matrices does a lot of unnecessary allocation and copying!
       map = graded_map(codom, gens(SM); check=false)
       dom = domain(map)
-      AbstractAlgebra.set_name!(dom, "$br_name^$rk")
     else
       codom = dom
       dom   = free_module(br, Singular.ngens(res[j]))
       SM    = SubModuleOfFreeModule(codom, res[j])
-      AbstractAlgebra.set_name!(dom, "$br_name^$rk")
       #generator_matrix(SM)
       map = hom(dom, codom, gens(SM); check=false)
     end
@@ -229,7 +221,6 @@ function _extend_free_resolution(cc::Hecke.ComplexOfMorphisms, idx::Int)
   # Finalize maps.
   if slen < len
     Z = FreeMod(br, 0)
-    AbstractAlgebra.set_name!(Z, "0")
     pushfirst!(cc, hom(Z, domain(cc.maps[1]), Vector{elem_type(domain(cc.maps[1]))}(); check=false))
     cc.complete = true
   end
@@ -457,11 +448,6 @@ function free_resolution(M::SubquoModule{<:MPolyRingElem};
     slen =  slen > length ? length : slen
   end
 
-  br_name = AbstractAlgebra.get_name(base_ring(M))
-  if br_name === nothing
-    br_name = "R"
-  end
-
   #= Add maps from free resolution computation, start with second entry
    = due to inclusion of presentation(M) at the beginning. =#
   j   = 1
@@ -474,7 +460,6 @@ function free_resolution(M::SubquoModule{<:MPolyRingElem};
       #ff = graded_map(codom, SM.matrix)
       ff = graded_map(codom, gens(SM); check=false)
       dom = domain(ff)
-      AbstractAlgebra.set_name!(dom, "$br_name^$rk")
       insert!(maps, 1, ff)
       j += 1
     else
@@ -483,7 +468,6 @@ function free_resolution(M::SubquoModule{<:MPolyRingElem};
       dom   = free_module(br, rk)
       SM    = SubModuleOfFreeModule(codom, res[j])
       #generator_matrix(SM)
-      AbstractAlgebra.set_name!(dom, "$br_name^$rk")
       insert!(maps, 1, hom(dom, codom, gens(SM); check=false))
       j += 1
     end
@@ -495,7 +479,6 @@ function free_resolution(M::SubquoModule{<:MPolyRingElem};
     else
       Z = FreeMod(br, 0)
     end
-    AbstractAlgebra.set_name!(Z, "0")
     insert!(maps, 1, hom(Z, domain(maps[1]), Vector{elem_type(domain(maps[1]))}(); check=false))
   end
 
@@ -531,7 +514,6 @@ function free_resolution(M::SubquoModule{T}) where {T<:RingElem}
       K, inc = kernel(map(C, i))
       nz = findall(x->!iszero(x), gens(K))
       F = FreeMod(R, length(nz))
-      iszero(length(nz)) && AbstractAlgebra.set_name!(F, "0")
       phi = hom(F, C[i], iszero(length(nz)) ? elem_type(C[i])[] : inc.(gens(K)[nz]); check=false)
       pushfirst!(C.maps, phi)
     end
@@ -562,7 +544,6 @@ function free_resolution_via_kernels(M::SubquoModule, limit::Int = -1)
         h = graded_map(domain(mp[1]), Vector{elem_type(domain(mp[1]))}(); check=false)
       else
         Z = FreeMod(base_ring(M), 0)
-        AbstractAlgebra.set_name!(Z, "0")
         h = hom(Z, domain(mp[1]), Vector{elem_type(domain(mp[1]))}(); check=false)
       end
       insert!(mp, 1, h)

src/Modules/UngradedModules/Presentation.jl

@@ -20,6 +20,7 @@ function presentation(SQ::SubquoModule;
   end
 
   # Old code left for debugging
+  #=
   #A+B/B is generated by A and B
   #the relations are A meet B? written wrt to A
   R = base_ring(SQ)
@@ -30,11 +31,6 @@ function presentation(SQ::SubquoModule;
     F = FreeMod(R, ngens(SQ.sub))
     h_F_SQ = hom(F, SQ, gens(SQ)) # DO NOT CHANGE THIS LINE, see present_as_cokernel and preimage
   end
-  br_name = AbstractAlgebra.get_name(R)
-  if br_name === nothing
-    br_name = "br"
-  end
-  AbstractAlgebra.set_name!(F, "$br_name^$(ngens(SQ.sub))")
   q = elem_type(F)[]
   if is_generated_by_standard_unit_vectors(SQ.sub)
     if isdefined(SQ, :quo)
@@ -86,32 +82,21 @@ function presentation(SQ::SubquoModule;
     G = FreeMod(R, length(q))
     h_G_F = hom(G, F, q)
   end
-  br_name = AbstractAlgebra.get_name(F.R)
-  if br_name === nothing
-    br_name = "br"
-  end
-  AbstractAlgebra.set_name!(G, "$br_name^$(length(q))")
   if is_graded(SQ)
     Z = graded_free_module(F.R, 0)
   else
     Z = FreeMod(F.R, 0)
   end
-  AbstractAlgebra.set_name!(Z, "0")
   h_SQ_Z = hom(SQ, Z, Vector{elem_type(Z)}([zero(Z) for i=1:ngens(SQ)]))
   M = Hecke.ComplexOfMorphisms(ModuleFP, ModuleFPHom[h_G_F, h_F_SQ, h_SQ_Z], check = false, seed = -2)
   set_attribute!(M, :show => Hecke.pres_show)
   return M
+  =#
 end
 
 function _presentation_graded(SQ::SubquoModule)
   R = base_ring(SQ)
 
-  # Prepare to set some names
-  br_name = AbstractAlgebra.get_name(R)
-  if br_name === nothing
-    br_name = "br"
-  end
-
   # Create the free module for the presentation
   #
   # We have to take representatives of the simplified 
@@ -124,14 +109,12 @@ function _presentation_graded(SQ::SubquoModule)
   F0_to_SQ = graded_map(SQ, gens(SQ); check=false)
   F0_to_SQ.generators_map_to_generators = true
   F0 = domain(F0_to_SQ)
-  AbstractAlgebra.set_name!(F0, "$br_name^$(ngens(SQ.sub))")
 
   K, inc_K = kernel(F0_to_SQ)
   F1_to_F0 = graded_map(F0, images_of_generators(inc_K))
   F1 = domain(F1_to_F0)
   #F1 = graded_free_module(R, [degree(x; check=false) for x in images_of_generators(inc_K)])
   #F1_to_F0 = hom(F1, F0, images_of_generators(inc_K), check=false)
-  AbstractAlgebra.set_name!(F1, "$br_name^$(ngens(F1))")
 
   # When there is no kernel, clean things up
   if is_zero(F1)
@@ -141,7 +124,6 @@ function _presentation_graded(SQ::SubquoModule)
 
   # prepare the end of the presentation
   Z = graded_free_module(R, elem_type(grading_group(R))[])
-  AbstractAlgebra.set_name!(Z, "0")
   SQ_to_Z = hom(SQ, Z, elem_type(Z)[zero(Z) for i in 1:ngens(SQ)]; check=false)
 
   # compile the presentation complex
@@ -155,24 +137,16 @@ end
 function _presentation_simple(SQ::SubquoModule)
   R = base_ring(SQ)
 
-  # Prepare to set some names
-  br_name = AbstractAlgebra.get_name(R)
-  if br_name === nothing
-    br_name = "br"
-  end
-
   # Create the free module for the presentation
   F0 = FreeMod(R, length(gens(SQ)))
   F0_to_SQ = hom(F0, SQ, gens(SQ); check=false)
   F0_to_SQ.generators_map_to_generators = true
-  AbstractAlgebra.set_name!(F0, "$br_name^$(ngens(SQ.sub))")
 
   K, inc_K = kernel(F0_to_SQ)
   @assert codomain(inc_K) === F0
   @assert all(x->parent(x) === F0, images_of_generators(inc_K))
   F1 = FreeMod(R, ngens(K))
   F1_to_F0 = hom(F1, F0, images_of_generators(inc_K), check=false)
-  AbstractAlgebra.set_name!(F1, "$br_name^$(ngens(F1))")
 
   # When there is no kernel, clean things up
   if is_zero(F1)
@@ -182,7 +156,6 @@ function _presentation_simple(SQ::SubquoModule)
 
   # prepare the end of the presentation
   Z = FreeMod(R, 0)
-  AbstractAlgebra.set_name!(Z, "0")
   SQ_to_Z = hom(SQ, Z, elem_type(Z)[zero(Z) for i in 1:ngens(SQ)]; check=false)
 
   # compile the presentation complex
@@ -202,7 +175,6 @@ function presentation(F::FreeMod; minimal = false)
   else
     Z = FreeMod(F.R, 0)
   end
-  AbstractAlgebra.set_name!(Z, "0")
   M = Hecke.ComplexOfMorphisms(ModuleFP, ModuleFPHom[hom(Z, F, Vector{elem_type(F)}()), hom(F, F, gens(F)), hom(F, Z, Vector{elem_type(Z)}([zero(Z) for i=1:ngens(F)]))], check = false, seed = -2)
   set_attribute!(M, :show => Hecke.pres_show)
   return M
@@ -608,21 +580,14 @@ function _presentation_minimal(SQ::ModuleFP{T};
                                minimal_kernel::Bool=true) where {T<:MPolyRingElem{<:FieldElem}}
 
   R = base_ring(SQ)
-
-  # Prepare to set some names
-  br_name = AbstractAlgebra.get_name(R)
-  if br_name === nothing
-    br_name = "br"
-  end
-
+
   SQ_new, phi = prune_with_map(SQ)
   F0 = ambient_free_module(SQ_new)
 
   # M_new is a quotient of a free module
   proj_map = hom(F0, SQ_new, gens(SQ_new), check=false)
   F0_to_SQ = compose(proj_map, phi)
   F0_to_SQ.generators_map_to_generators = true
-  AbstractAlgebra.set_name!(F0, "$br_name^$(ngens(F0))")
 
   is_sq_graded = is_graded(SQ)
 
@@ -638,7 +603,6 @@ function _presentation_minimal(SQ::ModuleFP{T};
     free_module(R, ngens(K))
   end
   F1_to_F0 = compose(hom(F1, K, gens(K), check=false), inc)
-  AbstractAlgebra.set_name!(F1, "$br_name^$(ngens(F1))")
 
   # When there is no kernel, clean things up
   if is_zero(F1)
@@ -647,7 +611,6 @@ function _presentation_minimal(SQ::ModuleFP{T};
     else
         F1 = FreeMod(R, 0)
     end
-    AbstractAlgebra.set_name!(F1, "$br_name^$(ngens(F1))")
     F1_to_F0 = hom(F1, F0, elem_type(F0)[]; check=false)
   end
 
@@ -657,7 +620,6 @@ function _presentation_minimal(SQ::ModuleFP{T};
   else
       Z = FreeMod(R, 0)
   end
-  AbstractAlgebra.set_name!(Z, "0")
   SQ_to_Z = hom(SQ, Z, elem_type(Z)[zero(Z) for i in 1:ngens(SQ)]; check=false)
 
   # compile the presentation complex